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How To Treat an Aquarium with Hyposalinity


Hyposalinity is a simple, effective, and natural way to help rid fish and fish-only aquariums of ich infestations, without harming the animals or the system. When the amount of salt in water is lowered, it results in a lowering of the "osmotic pressure" of the water as well, thus the related name Osmotic Shock Therapy (OST). Fish and a few other creatures can adjust to this change in pressure around them, but ich organisms cannot. Reduce this necessary pressure, and they literally explode!
Difficulty: Easy
Time Required: Varies

Here's How:

  1. Option A) Prepare a sufficient amount of 1.013 to 1.010 (specific gravity) range, tank pH and other water parameter matched saltwater to do a complete water change on a main aquarium, or to fill a QT with. Option B) Get a sufficient amount of appropriate source, tank pH matched freshwater ready for use.
  2. Option A) Remove about 3/4 of the saltwater in the aquarium and replace it with the prepared hyposalinity water. Option B) Drain about 1/2 of the saltwater out the aquarium and replace it with the freshwater.
  3. Test the aquarium water with a salinity tester or hydrometer, and if the salt level is still high, above 1.013ppm, or the freshwater level has become too low, below 1.010 (specific gravity), remove some of the water and top the tank off with whatever type of water is needed to bring the salinity level up or down to within the ideal range.
  4. Maintain the aquarium as a hyposalinity system for at least 3 weeks, 4 is better, and follow normal maintenance procedures using tank parameter matched hyposalinity water if and when water changes are needed.
  5. Final Phase Option A) For a main aquarium, once the treatment period is finished the salinity level needs to be returned to normal. HOWEVER, IF FISH OR OTHER ANIMALS ARE PRESENT, THIS HAS TO BE DONE GRADUALLY OVER A PERIOD OF DAYS, AS NOT TO SHOCK THEM! Start by removing about 1/4 of the hyposalinity water and replace it with regular level saltwater it had prior to treatment, such as 1.024ppm. Wait a day or two and repeat this process, and continue to do so until the salinity is back to normal.
  6. Final Phase Option B) If the main aquarium is being treated under hyposalinity, and the fish where removed and are also being treated in the same way in a QT, with the parameters of the aquarium and the QT water matched as closely as possible, the fish should be able to be placed directly back into the main aquarium, followed by Step 5 instructions above.
  7. Final Phase Option C) If the a main aquarium has no fish or other animals present, a complete water change can be done using normal level saltwater.


  1. Hyposalinity is most effective at "exploding" ich organisms when they are subjected to a "rapid" rather than a slow change in the osmotic pressure of the water around them, which is done by exposing them to a quickly lowered salinity environment.
  2. Hyposalinity is most effective at destroying ich organisms when they are most vulnerable, which is primarily during their newborn free-swimming phase of life, and before they are allowed to become mature parasites.
  3. Hyposalinity will kill delicate corals and invertebrates, therefore this treatment should NEVER be used in a reef tank system, unless these animals are removed!

What You Need

  • Prepared low salinity saltwater, or freshwater
  • Salinity tester/hydrometer
  • Water storage container

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